3.7.6 -  Insulation monitoring

In some special applications, usually IT systems, the insulation effectiveness of an installation or of an item of equipment is monitored continuously. This is done by the injection of a signal, usually at less than 50V, which measures insulation resistance. When this resistance falls below a preset level an alarm is triggered and/or the circuit concerned is switched off automatically. The setting of the monitor must be arranged so that it can only be altered by an authorised person, and to that end it must be possible to alter the setting only with a special tool.